verb

In the case of the Sun or some similar large object, as it contracts there is a decrease in its gravitational energy because the composite matter is moving closer to the middle, and that energy has to go somewhere.

The deer's range later contracted to the Ural Mountains, in modern-day Russia, which separate Europe from Asia.

On cooling it contracts to a smaller dimension, thus reducing the area of contact and allowing oxide to form at the interface.

1.1(Of a muscle) become shorter and tighter in order to effectmovement of part of the body:the heart contracts about seventy times a minute [with object]:exhale and slowly contract your abdominal muscles

Origin

Before railways were invented in the early 19th century, train followed a different track. Early senses included ‘a trailing part of a robe’ and ‘a retinue’, which gave rise to ‘a line of travelling people or vehicles’, and later ‘a connected series of things’, as in train of thought. To train could mean ‘to cause a plant to grow in a desired shape’, which was the basis of the sense ‘to instruct’. The word is from Latin trahere ‘to pull, draw’, and so is related to word such as trace (Middle English) originally a path someone is drawn along, trail (Middle English) originally in the sense ‘to tow’, tractor (late 18th century) ‘something that pulls', contract (Middle English) ‘draw together’, and extract (Late Middle English) ‘draw out’. Boys in particular have practised the hobby of trainspotting under that name since the late 1950s. Others ridicule this hobby and in Britain in the 1980s trainspotter, like anorak, became a derogatory term for an obsessive follower of any minority interest. Irvine Welsh's 1993 novel Trainspotting gave a high profile to the term. The title refers to an episode in which two heroin addicts go to a disused railway station in Edinburgh and meet an old drunk in a disused railway station who asks them if they are trainspotting. There are also other overtones from the language of drugs—track is an addicts' term for a vein, mainlining [1930s] for injecting a drug intravenously, and train for a drug dealer. Trainers were originally training shoes, soft shoes without spikes or studs worn by athletes or sports players for training rather than the sport itself. The short form began to replace the longer one in the late 1970s.